There has heretofore been known an intermittent aeration type activated sludge treatment process, wherein waste water is caused to flow into an aeration tank and aeration is repeatedly stopped and started in the aeration tank, whereby the waste water is treated.
According to the conventional intermittent aeration type activated sludge treatment process, in many of the operation control processes and the operation control unit, the starting and stopping of the aeration step is repeated in predetermined intervals of time by use of a timer or the like.
However, according to this process, there is a time duration for the aeration step and a time duration for stopping the aeration step which is fixed by the timer or the like, and there is no responsiveness to fluctuations in the flow rate of influent waste water and concentration of the activated sludge. More particularly, when the flow rate of influent waste water and the concentration of the activated sludge are low, a problem of excessive aeration is caused from the aeration at a constant rate, the quality of the treated water is deteriorated, and the rate of wasteful operating energy in the aeration device is notably high. On the other hand, when the flow rate of the influent waste water and the concentration of the activated sludge are high, the aeration becomes insufficient and the quality of the treated water is deteriorated.
The present invention has as its object the solving of the above-described problems in the intermittent aeration process.